Broader exception catching for ES collector http call

Change-Id: Ic03c518caf443636d5740680b3d55dae34c8a564
Adding new netapp Disk collector
thread-safety; some refactoring
Merge pull request #486 from rtoma/es-fix2

Broader exception catching for ES collector http call
Merge pull request #487 from peterfisher/master

New threaf-safe netapp collectors
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